where the colimit is with respect to the two functors (REF ) and (REF ).
We have a stratification into locally closed subsets (see [1]})
\(\Sigma (\mathcal {X})=\bigsqcup _{W_i\in \operatorname{Str}(\mathcal {X})} \sigma (W_i)^o/H_{W_i} \subset \overline{\Sigma }(\mathcal {X})=\bigsqcup _{W_i\in \operatorname{Str}(\mathcal {X})} \overline{\sigma }(W_i)^o/H_{W_i}\) 
